kern_sema.c revision 93818 
1/*
2 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice(s), this list of conditions and the following disclaimer as
9 *    the first lines of this file unmodified other than the possible
10 *    addition of one or more copyright notices.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice(s), this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
16 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
20 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
25 * DAMAGE.
26 *
27 * $FreeBSD: head/sys/kern/kern_sema.c 93818 2002-04-04 21:03:38Z jhb $
28 */
29
30/*
31 * Counting semaphores.
32 *
33 * Priority propagation will not generally raise the priority of semaphore
34 * "owners" (a misnomer in the context of semaphores), so should not be relied
35 * upon in combination with semaphores.
36 */
37
38#include <sys/param.h>
39#include <sys/systm.h>
40#include <sys/ktr.h>
41#include <sys/condvar.h>
42#include <sys/lock.h>
43#include <sys/mutex.h>
44#include <sys/sema.h>
45
46void
47sema_init(struct sema *sema, int value, const char *description)
48{
49
50	KASSERT((value >= 0), ("%s(): negative value\n", __func__));
51
52	bzero(sema, sizeof(*sema));
53	mtx_init(&sema->sema_mtx, description, "sema backing lock",
54	    MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
55	cv_init(&sema->sema_cv, description);
56	sema->sema_value = value;
57
58	CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
59}
60
61void
62sema_destroy(struct sema *sema)
63{
64
65	CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
66	    cv_wmesg(&sema->sema_cv));
67
68	KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
69
70	mtx_destroy(&sema->sema_mtx);
71	cv_destroy(&sema->sema_cv);
72}
73
74void
75_sema_post(struct sema *sema, const char *file, int line)
76{
77
78	mtx_lock(&sema->sema_mtx);
79	sema->sema_value++;
80	if (sema->sema_waiters && sema->sema_value > 0)
81		cv_signal(&sema->sema_cv);
82
83	CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
84	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
85
86	mtx_unlock(&sema->sema_mtx);
87}
88
89void
90_sema_wait(struct sema *sema, const char *file, int line)
91{
92
93	mtx_lock(&sema->sema_mtx);
94	while (sema->sema_value == 0) {
95		sema->sema_waiters++;
96		cv_wait(&sema->sema_cv, &sema->sema_mtx);
97		sema->sema_waiters--;
98	}
99	sema->sema_value--;
100
101	CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
102	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
103
104	mtx_unlock(&sema->sema_mtx);
105}
106
107int
108_sema_timedwait(struct sema *sema, int timo, const char *file, int line)
109{
110	int ret, timed_out;
111
112	mtx_lock(&sema->sema_mtx);
113
114	/*
115	 * A spurious wakeup will cause the timeout interval to start over.
116	 * This isn't a big deal as long as spurious wakeups don't occur
117	 * continuously, since the timeout period is merely a lower bound on how
118	 * long to wait.
119	 */
120	for (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) {
121		sema->sema_waiters++;
122		timed_out = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
123		sema->sema_waiters--;
124	}
125	if (sema->sema_value > 0) {
126		/* Success. */
127		sema->sema_value--;
128		ret = 1;
129
130		CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
131		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
132	} else {
133		ret = 0;
134
135		CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
136		    cv_wmesg(&sema->sema_cv), file, line);
137	}
138
139	mtx_unlock(&sema->sema_mtx);
140	return (ret);
141}
142
143int
144_sema_trywait(struct sema *sema, const char *file, int line)
145{
146	int ret;
147
148	mtx_lock(&sema->sema_mtx);
149
150	if (sema->sema_value > 0) {
151		/* Success. */
152		sema->sema_value--;
153		ret = 1;
154
155		CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
156		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
157	} else {
158		ret = 0;
159
160		CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
161		    cv_wmesg(&sema->sema_cv), file, line);
162	}
163
164	mtx_unlock(&sema->sema_mtx);
165	return (ret);
166}
167
168int
169sema_value(struct sema *sema)
170{
171	int ret;
172
173	mtx_lock(&sema->sema_mtx);
174	ret = sema->sema_value;
175	mtx_unlock(&sema->sema_mtx);
176	return (ret);
177}
178